Thanks Redwood and zem100, talking to a planner sounds like the right way to go. 

Redwood : This block is in Melbourne, under the Kingston council. Care to comment further?

I was really curious about the big gray area in the zoning clauses, etc online – there's coverage of subdivision, and coverage of 2 dwellings on a block, but no talk of minimum block size, etc. So – theoretically – on an 800sqm block, I could subdivide then build 2 units on each. Pretty sure that's not what the council has in mind but it looks perfectly plausible just going by the zoning schedules… I think due to bringing in the new zones in July 2014, this council just hasn't decided on a minimum block size yet? Hard for those of us without connections to the planners. But I will call and inquire.